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BLDC Motor Drive waveforms

Discussion in 'Electronic Design' started by Harry Dellamano, Aug 1, 2013.

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  1. Attached is a waveform of one winding of a three phase trapezoid drive
    motor with another phase PWM drive on the bottom. This 3 phase 4 pole motor
    is rotating at 1500 RPM with 120Vdc, 20KHz and about 8.0 amps peak on each
    winding. My drive electronics but someone else's (enemy) software.
    https://www.dropbox.com/s/p7yg8peujjkzvac/DSX_20130802022721.pdf
    My question, does that current waveform, on top, look correct? At 3k RPM it
    screams. Should not the top portion and bottom be similar?

    Regards, Harry
     
  2. Tim, you are the man! The sequence is fudged up. It should be at any driver
    output; 2/6 PWM, 1/6 float, 2/6 low to sink current, 1/6 open, then repeat.
    Mine has 1/6 low, 2/6 PWM, 1/6 float, 2/6 low. That is 3/6 low and only 1/6
    float. What a POS!
    Thanks Tim, Harry
     
  3. Here is a pic of current in one of the three phases from my crack software
    weenies.
    https://www.dropbox.com/s/sx7xn6m6w6mw60r/2000rpm 270V 775W Phase U.pdf

    This trapezoidal waveform has ripple current on the positive and negative
    peaks causing torque chatter. The SW boys say that is normal. (Sorry for the
    current offset in the pic. poor tech)
    What say anybody?

    Thanks Harry
     
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